Showing papers by "Kikuo Okuyama published in 2002"
TL;DR: In this paper, a simple technique for sizing colloidal particles by means of electrospray and aerosol techniques was developed, where the size distribution of different types of colloids (oxides, met...
Abstract: The goal of this work was to develop a simple technique for sizing colloidal particles by means of electrospray and aerosol techniques. Size distribution of different types of colloids (oxides, met...
143 citations
TL;DR: In this paper, the change in morphology of agglomerates consisting of nanometer primary gold particles was studied experimentally and theoretically, and the sintering time and the rate constant of restructuring were obtained.
115 citations
TL;DR: In this article, a spray-drying method was used to obtain a porosity of 70% for polystyrene latex (PSL) nanoparticles colloids, which were then atomized to form micrometer-sized droplets.
Abstract: Silica powder containing organized pores was prepared by a spray drying method. Silica and polystyrene latex (PSL) nanoparticles colloids were mixed and atomized to form micrometer-sized droplets. Nitrogen carrier gas was used to carry the resulting droplets into a vertical reactor that contained two heating zones: 200 °C and 450 °C, which were used, respectively, to evaporate the dispersing medium (water) and to decompose the PSL particles to give a porous silica powder. The pores on the surface of the powders were found to be arranged into a hexagonal packing, indicating that a self-organization process occurred spontaneously during evaporation of the solvent. The pore size was controlled by changing the size of the PSL particles. By adding an additional zone (third zone) maintained at high temperatures, the produced powders could be in-situ annealed. A comparison of the average volume of the powder before and after annealing (at 1500 °C) indicated that the porosity of the powder was about 70%. Togethe...
104 citations
TL;DR: In this article, the effects of process parameters on the properties of ZnS:Mn2+ particles were systematically investigated for Mn2+ doping concentrations of 0−8 at. %.
Abstract: Spray pyrolysis, an aerosol decomposition technique, was first used to synthesize ZnS:Mn2+ particles, and their optical properties were characterized. The effects of process parameters on the properties of ZnS:Mn2+ particles were systematically investigated for Mn2+ doping concentrations of 0−8 at. %. The results show that a number of parameters such as temperature, cationic source, doping concentration, solution composition, and concentration can affect particle morphology, crystalline phase, crystallinity, and thus the photoluminescence of the products. Micrometer/submicrometer particles have spherical shapes and dense microstructures. Excitation/emission bands and intensities are largely dependent on the synthesis temperature employed. The effects of different precursors on the product particles and photoluminescence were also investigated. Some of the phenomena observed differed from other reports. The mechanisms by which various process conditions affect particle morphology, crystalline phase, and lu...
81 citations
TL;DR: In this article, a new bipolar charger for nanometer aerosols using soft X-ray photoionization was developed, and the charging probability of nanoparticles was evaluated experimentally and theoretically.
Abstract: A new bipolar charger for nanometer aerosols using soft X-ray photoionization was developed. The concentrations and mobility distributions of the positive and negative ions generated by the X-ray charger were investigated, and then the charging probability of nanoparticles was evaluated experimentally and theoretically. All experimental data of the X-ray charger were compared with those of a 241Am α-ray bipolar charger. It was found that the X-ray bipolar charger could produce at least about 3.5 times as high concentration of gaseous ions as the α-ray charger and thus could have particles attain the equilibrium bipolar charging state in shorter residence time than the α-ray charger. The charging state of particles attained by the X-ray charger was explained by theoretical calculations as well as α-ray bipolar charging. It was concluded that the X-ray charger would be a useful instrument for charging high number concentration nanoparticles in the electrical aerosol measurements.
71 citations
TL;DR: In this article, a modified aerosol decomposition process was used to extract micrometer/submicrometer particles into nanosized particles in salt microreactors using NiO synthesis as a model.
Abstract: Nanoparticles were synthesized using a modified aerosol decomposition process. The goal of this work was to investigate the breakup of micrometer/submicrometer particles into nanosized particles in salt microreactors using NiO synthesis as a model. The influence of various operating conditions such as temperature, type of salt, salt composition, and concentration on the separation process were investigated. The results show that addition of inorganic salts leads to substantial changes in particles which are produced and that nanoparticles can be obtained under a variety of conditions. An optimum temperature range exists for nanoparticle separation. Different types of salts and precursors have great influences on the separation process as well as the characteristics of the products, which, along with synthesis temperature, can be used to control the properties of the final product.
37 citations
TL;DR: In this paper, the effect of shape and porosity of dense and porous spheroidal particles on electrical mobility was investigated using a laser particle counter coupled with a pulse height analyzer.
37 citations
TL;DR: In this paper, the behavior of fine particles in a low-pressure parallel plate chemical vapor deposition reactor was investigated by constructing a system that permits particle motion in the reactor to be visualized.
35 citations
32 citations
TL;DR: In this paper, the luminescent nanoparticles inside the polymer matrix are grown instead of dispersing the preparednanoparticles by a mixing process, as is currently used in conventional methods, allowing the sizes of thenanoparticles to be controlled by using different quantities of precursors as well as by adjusting the storage time prior to drying.
Abstract: Department of Chemical Engineering and Material Science, Henry Samuely School of Engineering,University of California, Irvine, California 92692, USAAn in situ method for the production of bright green, luminescent nanoparticles loaded polymer electrolytes is reported. Using thisapproach, the complicated multistep process, which is associated with existing methods can be replaced with only a single step.The single key step is growing the luminescent nanoparticles inside the polymer matrix, instead of dispersing the preparednanoparticles by a mixing process, as is currently used in conventional methods. This method also allows the sizes of thenanoparticles to be controlled by using different quantities of precursors as well as by adjusting the storage time prior to drying.This new class of materials has considerable potential for use in the preparation of devices that simultaneously produce bothelectrical current and light, such as luminescent electrochemical cells, self-powered displays, and related devices.© 2002 The Electrochemical Society. @DOI: 10.1149/1.1467369# All rights reserved.Manuscript submitted August 13, 2001; revised manuscript received November 11, 2001. Available electronically March 29, 2002.
31 citations
TL;DR: In this paper, the conductance of a circular tube of finite length was measured in the continuum and transition regimes for length to diameter ratios L / D ranging from 0.045 to 33.4 and pressure ratios across the tubes P 1 / P 2 from 1.1 to 23.
TL;DR: In this article, the effects of NO 2 on particle formation in SO 2 /H 2 O/Air mixtures by f -ray irradiation as a source of hydroxyl radicals are investigated to evaluate the contribution of homogeneous and ion-induced nucleation in the nanometer-sized aerosol particle generation.
Abstract: Effects of NO 2 on particle formation in SO 2 /H 2 O/Air mixtures by f -ray irradiation as a source of hydroxyl radicals are investigated to evaluate the contribution of homogeneous and ion-induced nucleation in the nanometer-sized aerosol particle generation. The total particle number concentration, the charged-particle fraction, and the electrical mobility distribution of particles and hydrated and solvated ions generated in NO 2 /SO 2 /H 2 O/Air mixtures were measured at NO 2 levels of 0-1.98 ppm, SO 2 levels of 0-3.87 ppm, and H 2 O levels of 6480-9889 ppm. Total particle number concen2 tration first tends to increase with increasing NO 2 concentration up to a certain NO 2 level and then decreases for NO 2 concentrations beyond this point. The charged-particle fraction, indicative of particle formation by ion-induced nucleation, tends to decrease with increasing NO 2 concentration, reaching a minimum value. The peak intensity of the electrical mobility distribution for particles significantly exceeded...
TL;DR: In this paper, the optimal conditions for the synthesis of nonagglomerated BaTiO3 particles by salt-assisted spray pyrolysis (SASP) were investigated.
Abstract: Optimum conditions for the synthesis of nonagglomerated BaTiO3 particles by salt-assisted spray pyrolysis (SASP) were investigated. The effect of particle residence time in the reactor and salt concentration on the crystallinity and surface morphology of BaTiO3 was examined by x-ray diffraction and scanning electron microscopy. Mixtures of a metal chloride or nitrate salt, dissolved in aqueous precursor solutions, were sprayed by an ultrasonic atomizer into a five-zone hot-wall reactor. By increasing the salt concentration or the particle residence time in the hot zone, the primary particle size was increased, and its surface texture was improved compared to BaTiO3 particles prepared by conventional spray pyrolysis. The SASP-prepared BaTiO3 crystal was transformed from cubic to tetragonal by simply increasing the salt concentration at constant temperature and residence time. Further thermal treatments such as calcination or annealing are not necessary to obtain nonagglomerated tetragonal BaTiO3 (200–500 nm) particles with a narrow size distribution. Increasing the carrier gas flow rate and decreasing the residence time in the hot zone resulted in cubic BaTiO3 particles about 20 nm in diameter.
TL;DR: In this article, a mixing-type condensation nucleus counter (MTCNC) was used to detect nanometer-sized particles suspended under low-pressure conditions, and the experimental results show that MTCNC is capable of measuring nanoparticles smaller than 10 nm at low pressures above 65 Torr (8.644 kPa ) by adjusting the rate of the aerosol flow, the amount of vapor and temperature depending on the desired operation pressure.
TL;DR: In this paper, the distribution and transport of fine particles trapped in a radio-frequency (rf) plasma-enhanced chemical vapor deposition reactor was investigated using a laser light scattering technique.
Abstract: The distribution and transport of fine particles trapped in a radio-frequency (rf) plasma-enhanced chemical vapor deposition reactor was investigated using a laser light scattering technique. Structured clouds of particles were observed at localized regions between the holes below the showerhead. Typically, at a high rate of gas flow, particles emerging from the showerhead holes overshoot the equilibrium position of the particle trap, and the particle clouds in the trap were small and thin (winding mode). At a low rate of gas flow, the particles are directly attracted to the trap locations, and large particle clouds (lumping mode) were observed. The particle number concentration of trapped particles tends to increase with increasing rf power and decrease with increasing particle size. When the gas flow rate is increased, a sharp decrease occurs at a certain flow rate.
TL;DR: In this article, carbon coating using a chemical agent to aid the carbon to adhere to the surface of metal particles was used to improve electrical resistance and orientation properties of magnetic recording media.
Abstract: Magnetic particles with finer size, higher coercive force, and lower electrical resistance are required to produce better magnetic recording media. Metal has become one of the most suitable materials for high-density magnetic recording media; however metal particles are chemically unstable and their magnetic properties such as coercive force and saturation magnetization are easily ruined. We have tried carbon coating using a chemical agent to aid the carbon to adhere to the surface of metal particles. The carbon-coated particles become chemically stable and their oxidation is gradual enough to extinguish the ignition point. Magnetic tapes prepared using the carbon-coated metal particles in the recording layer exhibit improvements in both electrical resistance and orientation properties. A decrease in the electrical resistance of about two orders of magnitude relative to conventionally prepared tapes is achieved when about 10% of the particle weight is carbon black. The squareness and orientation ratio are also raised and viscosity is lowered because the dispersibility of these particles in magnetic lacquer is better than that of the uncoated metal particles. Transmission electron microscopy photographs indicate that all of the carbon black is bound to the surface of the metal particles.
04 Mar 2002
TL;DR: Park et al. as mentioned in this paper extended the moment method of log-normal size distribution function to cover the low Knudsen number transition regime and used the harmonic mean method for obtaining the transition correction factors for mass and heat fluxes.
Patent•
15 Nov 2002
TL;DR: In this paper, a fine liquid droplet producing device for atomizing a liquid pumped from a sample container by a fixed-displacement pump to produce fine liquid liquid droplets suspended in a carrier gas was described.
Abstract: A liquid-suspended particle analyzer includes: a fine liquid droplet producing device for atomizing a liquid pumped from a sample container by a fixed-displacement pump to produce fine liquid droplets suspended in a carrier gas; an evaporator for evaporating the liquid parts of the fine liquid droplets to produce an aerosol of the carrier gas and particles suspended in the carrier gas; a differential mobility classifier for classifying the particles of the aerosol by particle size according to mobility; and a Faraday cup electrometer for counting the respective numbers of the particles of the particle groups classified by particle size by the differential mobility classifier so as to determine the respective particle concentrations of the groups. The fine liquid droplets producing device includes an electrospraying device adapted to convert the liquid supplied by the liquid supply device into charged fine liquid droplets; and an atomizer adapted to suspend the charged fine liquid droplets produced by the electrospraying device in the carrier gas.
Patent•
14 Nov 2002
TL;DR: A liquid-suspended particle analyzer includes: a fine liquid droplet producing device for atomizing a liquid pumped from a sample container by a fixed-displacement pump to produce particles suspended in a carrier gas; an evaporator for evaporating the liquid parts of the fine liquid liquid droplets to produce an aerosol of the carrier gas and particles suspended inside the gas; a differential mobility classifier for classifying the particles of the aerosol by particle size according to mobility; and a Faraday cup electrometer for counting the respective numbers of the particles classified by particle
Abstract: A liquid-suspended particle analyzer includes: a fine
liquid droplet producing device for atomizing a liquid pumped
from a sample container by a fixed-displacement pump to produce
fine liquid droplets suspended in a carrier gas; an evaporator
for evaporating the liquid parts of the fine liquid droplets
to produce an aerosol of the carrier gas and particles suspended
in the carrier gas; a differential mobility classifier for
classifying the particles of the aerosol by particle size
according to mobility; and a Faraday cup electrometer for
counting the respective numbers of the particles of the
particle groups classified by particle size by the
differential mobility classifier so as to determine the
respective particle concentrations of the groups. The fine
liquid droplets producing device includes an electrospraying
device adapted to convert the liquid supplied by the liquid
supply device into charged fine liquid droplets; and an
atomizer adapted to suspend the charged fine liquid droplets
produced by the electrospraying device in the carrier gas.
TL;DR: In this article, a flow-cell type optical particle counter based on light scattering method was developed for real-time measurement of particles in semiconductor material gases, which enabled direct and in-line measurement of the particles in the material gases for the first time.
Abstract: Improvement of semiconductor integration requires the contamination control of finer particle in semiconductor manufacturing processes. In particular, the control of particle contamination in semiconductor material gases is important for enhancing the production yield. A flow-cell type optical particle counter based on light scattering method was developed for real-time measurement of particles in semiconductor material gases. In this paper, the flow-cell type particle counter was inserted in gas supply lines of semiconductor manufacturing processes. This enabled direct and in-line measurement of particles in the semiconductor material gases for the first time. The measurements showed that the concentration of particles in semiconductor material gases depended on the material and condition of gas cylinders and gas filters. The particle concentration was also affected by the operation of gas supply systems. It was suggested that there was a considerable amount of particulate contaminant generation in the semiconductor gases. The measured results for inert gases were significantly different from those of the semiconductor gases. Consequently, the importance of the direct and in-line measurement was confirmed.
TL;DR: In this paper, the dependence of UF5 nanoparticles size distribution on growth time was investigated for various initial concentrations of uF5 monomers, and an analysis using Lee's coagulation model revealed that the growth mechanism involved a Brownian coagulated process and that the sticking probability of the nanoparticles was approximately unity.
Abstract: The dependence of UF5 nanoparticle size distribution on growth time was investigated for various initial concentrations of UF5 monomers. UF5 nanoparticles prepared by photodissociation of UF6 in a mixed-flow reactor were allowed to pass through a plug-flow reactor (PFR), and their size distribution was measured by an in-situ size-monitoring system, namely a low-pressure differential mobility analyzer. By changing the length of the PFR, the growth time in the PFR was controlled from 0 to 30 s. An analysis using Lee’s coagulation model revealed that the growth mechanism of the UF5 nanoparticles involved a Brownian coagulation process and that the sticking probability of the nanoparticles was approximately unity.
Patent•
14 Nov 2002
01 Jan 2002
TL;DR: In this paper, the conductance of nitrogen gas through a circular tube of finite length was measured in the continuum and transition regimes for length to diameter ratios L=D ranging from 0.045 to 33.4 and pressure ratios across the tubes P1=P2 from 1.1 to 23.
Abstract: The conductance of nitrogen gas through circular tube of $nite length was measured in the continuum and transition regimes for length to diameter ratios L=D ranging from 0.045 to 33.4 and pressure ratios across the tubes P1=P2 from 1.1 to 23. A numerical analysis was carried out to estimate the conductance using the continuum approach in the continuum regime and transition regime at low Knudsen number, and using direct simulation Monte Carlo (DSMC) method in the transition regime at high Knudsen number. The observed conductances were compared with the simulation and an empirical equation derived by Hanks–Weissberg. Both the experimental and simulation results show that the conductances at a constant gas %ow rate increases linearly with increasing arithmetic mean pressure across the tube Pav =( P1 + P2)=2, irrespective of the P1=P2 ratio. The observed conductances were smaller than those predicted by the Hanks–Weissberg’s equation. The deviation increases with increasing gas %ow rate, and with decreasingL=D ratio. It was con$rmed that the deviation occurs due to the increase in the e=ects of inertia and expansion in the %owing gas with increasing %ow rate and decreasing L=D. A semi-empirical equation was derived by substituting the Poiseuille term in the Bernoulli formula with Hank–Weissberg’s equation under the condition of isothermal expansion. The proposed equation was found to be valid in the range of the continuum regime to the transition regime at low Knudsen number. ? 2002 Elsevier Science Ltd. All rights reserved.